Frost might have a use or two in BRF, but fire and arcane scales amazingly well.
Arcane and fire can get their best stats on most of the BRF gear, and will for sure be the go-to specs for progression in BRF.
Until 4 set fire, arcane will most likely be the go-to spec.
Arcane does absolutely silly single target - it is indeed broken. But let's enjoy it ^^